This application claims the priority of Germany, filed Sep. 13, 2002, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and a system for visually detecting deviations in paint gloss according to the preamble of claim 1.
From European Patent Document EP 0 286 994 A2, a method and a system are known for detecting surface defects, preferably for detecting paint defects on the surface of a motor vehicle body. By means of an illuminating system, a streak of light is generated on the surface, and this streak of light is guided by means of a relative movement between the illuminating system and the surface over this surface, and streak-shaped sections of the surface of the objects are in each case recorded in steps in the area of the light streak. Further, from International Patent Document WO 98/08078, a system for the visual inspection of the surface finish of matching surfaces is known, particularly of painted vehicle bodies, by means of several illuminating elements whose main beaming direction extends in each case at slanted angles with respect to the matching surface.
It is an object of the invention to provide an improved method and a system for visually detecting deviations in paint gloss, particularly a fogginess or mottling of the paint of a surface coating of a vehicle.
According to the invention, this object is achieved by means of the method characteristics of claims 1 and 2 as well as by means of the system characteristics according to claims 3 to 12.
The principal advantages achieved by means of the invention are that a visual detection of irregularities of the vehicle paint coat takes place as early as in the initial stage and corresponding correction measures can be taken for eliminating the defects. For the visual detection of these irregularities, such as fogginess and mottling of the paint, the outer surfaces of the two vehicle sides as well as additional surfaces of the forward and rearward vehicle body are illuminated by beams of light in a partially areal manner and, at a distance from the vehicle at predefined viewing ranges and defined viewing positions, these surfaces are judged on a marked path. The marked path consists of a semicircle on the lateral surfaces of the vehicle and an adjoining segment of a circle on the forward and rearward vehicle body. On this path, the viewing positions are assigned to the light beaming devices, in which case, additional positions for looking at the vehicle surfaces exist between the viewing positions on the marked path. As a result, it is advantageously achieved that the fogginess and the mottling respectively of the paint can be detected at all. The reason is that it is not only the illumination which is decisive but also the judging distance and the viewing positions with respect to the vehicle. Only when the entire surface to be judged can be seen as a whole, can the fogginess and mottling in the surface of the vehicle body be detected.
It was found that, because of the physical conditions, the amount of paint which can be sprayed onto vertical surfaces (for example, doors) is always less than the amount which can be sprayed onto horizontal surfaces (for example, the hood). As a result of the insufficient layer thickness of the coloring paint (base paint), fogginess and mottling will then be visible mainly on the sides of the vehicle body. In normally illuminated factory hangars, paint shop lines and even at well illuminated test sites, vehicle bodies with foggy and mottled paint coats can hardly be detected.
In order to remedy this condition, the light beaming devices are arranged at a distance with respect to both sides of the vehicle, in each case, in the longitudinal vehicle center plane for the lateral vehicle surfaces and in the transverse vehicle center plane for the forward and rearward vehicle body. The viewing positions are arranged on the marked path directly behind the light beaming devices in the transverse vehicle center plane, and the additional viewing positions for the light beaming devices assigned to the forward and rearward vehicle body are provided in the longitudinal vehicle center plane in each case on both sides of these light beaming device on the path. In particular, the light beam of the respective light beaming device should impinge approximately in the center of the forward and rearward vehicle body respectively as well as of the lateral vehicle surfaces, and the light cones of the light beaming devices comprise the entire length of the lateral vehicle surfaces and that of the forward and rearward vehicle body. The viewing range from the lateral viewing positions on the marked path, on the one hand, (word missing—translator) onto the entire lateral vehicles surfaces and, on the other hand, these viewing ranges overlap with the viewing ranges from the forward and rearward viewing positions on the forward and rearward vehicle body.
As a result, it is achieved that, on the one hand, by way of a light beaming device of each vehicle side, which in each case is arranged in the center, as well as on the forward and rearward body structure of the vehicle, first the entire surface to be judged is illuminated and can be viewed from predetermined viewing positions. When assessing paint surfaces on vehicle bodies, it was found that even slight parameter deviations at certain light conditions prove to be a serious defect. For example, if the door filler paint coat was machined (ground) because of a dust particle and subsequently the coloring base paint (for example, silver metallic) has a smaller layer, a light spot will appear in the door later when subjected to direct sun radiation. If the layer thickness is much too low, the spot will be clear and strong at its edges. When there is only a slightly smaller underlayer, the edges of the ground paint will be indistinct and therefore harder to be discerned by the customer.
For the further partial judging of the paint surface of the vehicle sides as well as of the forward and rearward vehicle body, two light beaming devices are provided for each vehicle side, whose cones of light overlap on the lateral surfaces, and the lateral vehicle surface as well as the surfaces of the forward and rearward vehicle body can be illuminated to the longitudinal center plane of the vehicle. The viewing positions are the same as in the case of only one light beaming device, these being provided on the marked path for each vehicle side in each case behind the two light beaming devices in the transverse vehicle center plane, and the viewing range in each case extending along a partial area of the lateral surface and overlapping with the viewing ranges from the forward and rearward viewing positions on the lateral surfaces.
So that an exact illumination of the vehicle surface to be assessed can take place, the light beaming devices for the lateral vehicle surfaces are aligned such that the light beam is oriented approximately at an angle of 90° with respect to the ground surface and impinges laterally on the surface to be checked, and the light cone extends in the vertical direction approximately from the vehicle side member to the belt line of the vehicle. The light beaming device on the rearward and forward vehicle body is aligned such that the light cone is aligned approximately in the center at an angle with respect to the ground surface and, in the case of the rearward vehicle body impinges in the vertical direction on an upward-curved area of the rear part, and the light cone covers (something is missing in the German—translator) in the lower edge of the rear window. In the case of the forward vehicle body, the line cone comprises the forward hood area in the vertical direction.
By means of the invention, an assessment of the fogginess and mottling takes place according to a defined standardized method with defined system elements, such as a illuminating system. For the assessment, it is provided according to the invention that, on the one hand, the viewing positions are defined on the marked path and, on the other hand, the judging person walks at a defined distance on the path around the vehicle in order to check the surface to be assessed.
In principle, the judging of the fogginess/mottling does not take place exclusively from one or more viewing positions but (the fogginess/mottling? translator) becomes more conspicuous when the person making the assessment is moving. Fogginess and spots in a paint coat occur only in the case of metallic paint coats. The conspicuous shadings result from metal particles (called bronze) situated in different directions. If one now moves along a vehicle body painted in a foggy/mottled manner, the conspicuousness rises many times over because the human eye subconsciously perceives mainly the light/dark change. One of the reasons why a movement should take place during the assessment is the fact that only extreme fogginess can be shown photographically. In contrast, the producing of a video film, like a movement, permits the recording of even slight fogginess/mottling.
So that an optimal judging of the fogginess/mottling can take place, not only the setup and sequence of the checking, but also a categorization according to a so-called ten scale is important. Since, during the checking, a certain subjectivity should still be considered, it is recommended that the checking be carried out by a team of experts. This means in practice that at least three experts from the fields of production, finishing and quality assurance judge individually and subsequently the individual results are used to take the average.
The ten scale describes the assessment categories, Point 1 being a good value and Point 10 being a poor value:                (1) No fogginess/mottling can be detected;        (2) only a very slight graining of the paint coat can be detected;        (3) homogeneous indistinct graining can be detected;        (4) uniform graining can be detected in the paint coat;        (5) slight shading or light indistinct spots can be detected;        (6) extreme shading or clearly defined spots can be detected (defect images of Steps 6 to 10 are relevant with respect to refinishing and customers);        (7) easily detectable shading or clearly defined spots; defects can be recorded photographically;        (8) shading or spots which are difficult to detect in neon light (2,000 lux);        (9) shading or spots which can easily be detected in neon light (2,000 lux);        (10) shading/spots which are immediately conspicuous in neon light (2,000 lux).        
An embodiment of the invention is illustrated in the drawings and will be described in detail in the following.